Furnace



y 1941} R. SHELLENBERGER I ,76

FURNACE Original Filed April 16, 1937 (5 Sheets-Sheetl Fig] INVENTOR.

Rolfe ghellenber ger y 1941- R. SHELLENBERGER 2,242,762

' FURNACE Original Filed April 16, 1937 6 Sheets-Sheet 2 INVENTOR.

Rolfe She/[en bergefi ORNEY.

y 1941- R. SHELLENBERGER ,7 2

I FURNACE Original Filed April 16, 193'! 6 Sheets-Sheet 3 y 1941- R.SHELLENBERGER 2,242,762

FURNACE Original Filed April 16. 1937 6 Shets-Sheet 4 Kw 9 m N10 n V6mfl 8 "M e H M y 1941- R. SHELLENBERGER 2,242,762

FURNACE Original- Filed April 16, 1937 6 Sheets-Sheet 5 I A MENTOR. Q0/749 She/[emberger x g ATTORNEY.

y 1 R. SHELLENQBER'GER' 2,242,762

FURNACE Original Filed April 16, 1937 6 Shgets-Sheet 6 INVENTOR. Ra/feShel/en bergen SQSEAETTOIRNEY.

Patented May 20,.i'94i v FURNACE Rolfe Shellenberger, Westfleld, N. J.,assignorfto The Babcock & Wilcox Company, N. J., a corporation of NewJersey Newark,

Application April 16, 1937; "Serial No. 137,158 Renewed July 13,'1939 7L23 Claims.

The present invention relates in general to the construction andoperation of furnaces for burning finely divided solid fuel insuspension, and

ture section of the' furnace and the convection heated steam generatingtubes from radiant heat from the primary or high temperature sectionwhich is the main combustion zone. The furnace screen further serves topromote mixing of the unburned gases leaving the high temperaturesection and also to collect ash particles 'in suspension from thefurnace gases before reaching the convection heated'surface.'

In accordance with my invention a two-stage pulverized fuel burningfurnace is providedhaving the furnacesections constructed and relativelyarranged and the furnaceslag screen constructed and arranged so that theprimary or high temperature section will have a normal toprovideshieldedopenings for the continuous discharge therethrough of molten slag fromthe high temperature section into an ash pit below the low temperaturesection.

The low temperature section is constructed and relatively arranged withrespect to the furnace screen and convection tube bank thatthetemperatures of the furnace gases and suspended ash particles will bereduced by radiant heat transfer therein to the temperature required atthe furnace exit for minimum fouling of the boiler tubes. The lowtemperature s'ection'has a substantially larger volume thanthe hightemperature section and this large unobstructed volume causes asubstantial reduction in furnace gas velocity. The resulting lowvelocity flow in and vertical arrangement of the low temperature sectionmaterially contributes to the separation of additional slag particles insuspension from the ascending furnace gases, augmenting the ash recoveryfrom the high temperature 'section. The low temperature conditions inthe secondary section cause the ash separating therein to be mainly in asolid or dry" state. The ash so separated drops into an ash hopperreceiving the molten slag flowing through the furnace screen openingsand is similarly handled.

mean temperature therein permitting the emcient and stabilizedcombustion of awide range of pulverized fuels, including bituminouscoals of almost any volatile, ash or sulphur content, or ash fusiontemperature,- with low carbon loss, over a wide range of operation. Thetemperature conditions normally maintained facilitate the separation ofa high percentage of the ash content of the fuel in the high temperaturesection and permit its continuous removal from this section as moltenslag, a type of ash elimination which is not only most conducive to highcombustion eificiencies but results in the least amount of ash beingcarried in suspension into the boiler gas passes and to the stack.

The furnace screen is constructed to almost entirely enclose that sideof the high temperature section with refractory surface andcorrespondingly shield the secondary or low temperature section fromradiant heat from the high temperature section, leaving only relativelynarrow passages through the screen to the low tempera.-

ture section, through which the gases pass after The general object ofthis invention is the provision of an improved construction of atwostage pulverized fuel furnace and a method of operating the samewhich is characterized by its adaptability for burning a wide range offuels at high efliciencies over a wide range of operation, the recoveryof a high percentage of the fuel ash content in the furnace, and thecontinuous removal of the ash recovered mainly in a molten state, Afurther object is the rovision of an improved furnace screenconstruction for a two-stage furnace which is character-.

a part of this specification. For a better under-' standing of'theinvention, its operating advantages and specific objects attained by itsuse, reference shouldbe had to the accompanying drawings and descriptivematter in which I have illustrated and described apreferred embodimentof the invention.

' In the drawings: t

Figs. 6, 7, and 8 are enlarged views of different portions of thefurnace walls shown inFig. 4:

F s. 9, 10 and 11 are vertical sections through different portions ofthe furnace screen taken on the lines 99, Iii-l 0, and l l-l|respectively, of Fig. 4; 7

Figs. 12, 13 and 14 are horizontal sections through one half of thefurnace screen taken Fig. 15 is a rear view of one of the slag drainopenings taken on the line 15-15 of Fig. 14;

Fig. 16 is a rear view of a portion of the furnace screen taken on thelin iii-l6 of Fig. 9;

Fig. 17 is an enlarged transverse section through the bafiie section ofthe furnace screen taken on the line Il-ll of Fig. 2;

Fig. 18 is a front view of the metallic parts of the baffle section ofthe furnace screen; and

Fig. 19 is a view similar to Fig. 18 with the tube studs omitted.

' The steam boiler unit illustrated in Fig. 1 comprises a furnace Illreceiving a supply of pulverized fuel and primary air from one or morepulverizers II, and preheated secondary air from a forced'draft fan l2and air heater 2|. The pulverized fuel is burned in suspension in atwostage furnace chamber having a primary or high temperature sectionl3, and a secondary or low boiler circulator and baiile tubes.

their loopedends supported from the adjacent The high temperaturesection of the furnace chamber is defined by a vertical front'wall 25,

. rearwardly and upwardly inclined arch 26, vertical side walls 21 andrearwardly and downwardly inclined floor 28, all of which are fluidcooled. For thispurpose a row of water-tubes extends upwardly along theinner sideof the front wall from a transverse front header SI andacross-the arch 26 to a transverse intermediate header 32. A row ofwatertubes 33 extends vertically along the inner side of each side wall21 between a lower longitudinal header 34 and a shorter upper header 35.A row of tubes 36 slopes downwardly along the floor from the header 3|to a parallel transverse header 3'! below the rear end of the floor.The'tubes 30,

33, and are of the fully studded type shown. in

Fig. 6, with the metallic studs and intertube spaces covered byinitially plastic refractory to' provide refractoryfaced boundarysurfacesfor the high temperature furnace section. The refractorycovering on th floor tubes is applied so astoform a flat slightlysloping floor shown in Figs. 2 and 3. u as The studs and refractory areomitted from a section of the tubes 30 in the arch to providetemperature section I4 as hereinafter described.

The furnace section I 4 is positioned directly below a sectional headersteam boiler having a high circulation head and comprising a bank ofinclined steam generating tubes l5 extending across the upper end of thefurnace section l4.

The tube bank I5 is connected at opposite ends.

space above the 'tube bank I5 is divided into two parallel gas passes22, 23 by a battle 11 carried on a row of supporting tubes ll extendingbetween the downtake end of the tube bank and the drum IS. A superheaterl8 having two superposed sections is arranged in the gas pass 22, and anupflow economizer l9, also. divided into two-superposed sections, hasits upper section extending through the baffle ll into both gas passes,while its lower section is confined to the gas pass 23. Dampers 20control the gas flow through the parallel gas passes, permittingvariable by-passing of the heating gases around the superheater toprotect the superheater at starting-up and provide an effectivesuperheat control over a wide range. The air heater 2| extends acrossthe portion of the setting above ature maintained. The

'high temperature furnace section,

a rectangular opening therein registering with the discharge end of asectional secondary air box 40 receiving preheated air from the airheater. A group of staggered pulverized fuel burners 4|, each of themultiple stream turbulent discharge type and receiving a mixture ofpulverized fuel and primary air from the pulverizer ll, extenddownwardly through corresponding compartments and in alignment withprotected portions of the tubes 3!) to discharge streams of pulverizedfuel and primary air against the tubes and thence downwardly through theintertube spaces into the furnace section I3. This location of the fuelburners provides a long 'J-shaped path of gas travel through thecontiguous sections ofthe furnace before reaching the boiler tubes I5.

The described construction of the high temperature section and thefurnace screen construction hereinafter described define a hotcombustion zone wherein pulverized fuel may be burned in suspension athigh rates of heat release and a normal mean furnace temperaturesubstantially above the fuel ash fusion temperhigher the rate of heatand consequently the more rapidly ash particles will be released andcoalesce'in the burning fuel stream. The

ash particles are separated from the descending fuel stream by gravityand by the substantial change in direction in the lower part of the anda layer of molten slag collects on substantially the entire area of therefractory floor 28. A large amount of ash will also deposit on'and flowdown the vertical front and side walls of the front section causingthese walls to become wet and sticky in operation. The wall constructiondescribed insures adequate protection of the furnace wall tubes, andpermits even high fusion temperature ash to be maintained in a moltencondition at relatively low furnace ratings. The high furnacetemperatures normally maintained in operation substantially contributeto the high comin the airbox 40 with their elonfurnace construction.'ihe rear side of the high temperature section ofthefurnacechamberisdeilnedbyafurnace than efiiciendcs We s the descri screen, thehigh temperature side of which is entirely covered by refractory.providing a boundary surface for the rear side of the high temperaturesection of similar character to its front and side walls. The furnacescreen is fluid cooled .by a single row of vertically extending watertubes 45 having their lower ends connected to the header 3'! and theirupper ends to the header '2.

spaced points in thesl8-8 screen row at the rear of the bends in thetube portions 45", 45, and

45. Vertically elongated ports 6| of different lengths are thus providedat transversely spaced The upper portions of all of the screen tubes 45are arranged in lateral alignment with the intertube spaces entirelyclosed ashereinafter described to form in eifect a fluid .cooled baiile46 extending from the rear end of the arch 2' downwardly and rearwardlyfor about half the height of this section. As shown in Figs. 17 to 19,the

front or high temperature side. of the tubes 45 have metallic studs 4'!welded thereon with some of the studs extending into the intertubespaces and the studs covered and intertube spaces closed by refractorymaterial. Adjacent 'tubes are secured together by welding some ofthestuds to vertically spaced tie plates 4'! in the intertube spaces. Theundulating refractory surface thus formed across the'high temperatureside of the baille 48 substantially contributes to the maintenanoe ofthe desired high temperature conditions in the high temperature section.

' The lower portions of the tubes 45 below the points in the plane ofthe tube portions 45. The furnace gases reach the ports 6l by aroundboth sides of the corresponding bent tube vertically elongated ports IFig. 12. The furnace gases receive changes in direction flowing throughthe gas r a thus formed. and the resultant m x s expedites thecombustion of any unburned fuel particles or gases. Thebent tubeportions substantially prevent heat radiation from the high temperaturesection through the corresponding screenopenings 5| in planes normal tothe plane of the tube row. As shown in Figs. 3 and 16, only narrowslot-like portions'of the screen gas passages appear when viewed fromthe high temperature section normal to the plane of the tube row.

The openings 6| behind the bent tube portions 45 terminate at theirlower ends above those hehind the tube portions 45'', except for thenarrow slots between adjacent pairs of tubes. The

baille 48 are arranged to form a slag screen 60 having a series oftransversely spaced vertically elongated gas flow passages or portsthroughwhich the high temperature gases from the front section flow at ahigh velocity into the rear or low temperature section of the furnacechamber. The gas flow passages are formed by bending alternate pairs ofthe tubes 45 forwardly, as shown in Figs. 9-14,.out of the plane of thetube row. As shown in Fig. 5, the slag screen portions of all of thetubes G5 are provided with studs 48 throughout their periphery, thestuds 48' extending into the intentube space of each pair being longerthan the others, and refractory entirely enclosing eachpair ofassociated tubes.

The row of tubes 55 have slag screen portions of several shapes; pairsofstraight tube po'rtions tfi 'which extend vertically from the lower endof the baiiie 48 to the rear edge of the floor 28; pairs of bent tubeportions 65* which are symmetrically bent forwardly and then rearwardlyin alignment withthe tubes '45 at the rear edge of the floor, as shownin Fig. 10; bent tube portions 45 which are bent forwardly like the tubeportions 85 and bent rearwardly into alignment with the tube portions 45above the rearward bend in the tube portions 45, as shown in Fig. 11;and pairs of tube portions 85 which follow the shape of the tubeportions 45" except at their lower ends, each pair of the portions 45having their lower ends bent rearwardly in a plane oblique to .the planeof the tube portions 45" below the lower bend in the tube portions 45and passing through the floor forwardly of its rear end, as shown inFigs. 9 and 14. One of the tube portions 45 adjacent each pair of tubesmolten slag continuously flows through these.

openings at the rear of the tube portions terminate near but slightlyabove the floor level, while the openings at the rear of the obliquelyarranged tube portions 45 and 45 have their lower ends at the floorlevel. Refractory ledges 63 are formed on the floor in the spacesbetween the tube pairs 45, 45 and 45, to provide a low damat the rearedge of the floor except between the oblique tube portions 45 and theadjoiningstraight tube portions 45 which space is used c as aslag drainopening 62. Onlytwo such slag drain openings 82' are provided in thescreen, with the openings symmetrically arranged at opposite sides ofthe center line of the furnace. The

drain openings in normal operation, and the fully studded refractoryconstruction adequately-protects the adjoining screen tubes from theiiowing slag. The high gas velocities and highly molten condition of theslag keep the slag drain openings from clogging. obliquely arranged Iopenings 6? in the side walls atthe rear of the screen permit theinsertion of implements for cleaning the corresponding slag drainopenings.

If for any reason the slag level should abnormally increase, forinstance, if the slag drain floor level, except below the two slagdrain'openings, have tube blocks 64. At the slag drain openings plasticrefractory is used, as shownin Fig. 16. A row of breaker blocks 65 onthe 45 is-bent forwardly adjacent its lower end in screen tubes extendsentirely across the rear side of the floor below the blocks 64 fordeflecting the descending slag away from the header 8'! into a hopper 55through which it drops into the pit 56 where it is quenched in a waterpool. The high velocity furnace gas flow through the screen gas flowpassages in conjunction with the changes in direction to which they aresubjected in entering and passing through the screen causes ashparticles in suspension to be deposited on the high temperature side ofthe slag screen and any unburned fuel particles and gases to be fur thermixed with the combustion'air and the combustion thereof rapidlycompleted. On leaving the slag screen the gases flow upwardly through Ithe rear low temperature section l4 of the furnace chamber.

The rear or low temperature section I4 is provided with a large amount'of cold wall area to permit the maintenance of a normal meantemperature therein below the fuel ash fusion temperature. As shown, therear section side wall tubes 33 below the baflle46 are onlypartlystudded, with refractory filling the intertube spaces, as shown inFig. 7, while the upper portions of the rear side wall tubes and tubesalong the rear wall 29 have metallic blocks clamped thereon to form fiatvertical wall surfaces, as

, shown in Fig. 8. The headers 35 and the upper ends of-the side walltubes rearwardly of these headers are connected to upper headers 51adjacent the tube bank l5.

The tubes '10 extend downwardly from a header 12 along the rear wall,with their lower portions extending downwardly and forwardly along aninclined hopper wall 14 to a lower header 13. The inclined wall section14 has a nose portion at its lower end along which are arranged atransverse row of breaker blocks 15. A row of tubes 16 extends upwardlyand forwardly from the header 32 to define a steeply inclined frontwall' for the rear section. The tubes are covered by blocks 11,constructed as-shown in Fig. 8, with a transverse row of breaker blocksI8 at their lower ends. a The front wall'of the hopper 55 below theheader 3'! and opposite the hopper wall 14 is protected by block coveredtubes 19 extending between the header 31 and a parallel misses sion. Thesteeply inclined upper portion of the arch and'of the bailie 46, and theuse of smooth metallic blocks to define their rear sur-' faces causesthese parts to remain clean in op eration and exert a substantialcooling effect on the gases and particularly the ash particles ascendingthrough the rear section. The low temperature furnace section I4 is thusmainly defined by bare metallic heat absorbing surface.

Any radiation from the front section throughv the furnace screenopenings will be to the lower I to the surrounding heat absorbingsurface. The

lower header 80. A row of spray nozzles 8| extends between the tubes I9and directs a water spray downwardly across the hopper 55. A row ofbreaker blocks 82 protect the nozzles 8|. The

- headers 34, 35, 51, l2, l3, and 80 are suitably connected into theboiler circulation system by external supply connections, some of whichare shown in Fig. 4, to provide an adequate supply elongated clampmember bearing against a pair of elongated supporting lu'gs 5| extendingalong and welded to the tubes 45. As shown in Fig. 19, the lugs 5| arewelded along their ends only and the ends of the clamp member 50 roundedto permit the clamp member to be installed or removed through the lowtemperature side of the baflle. The clamp is inserted until at the frontside of the lugs 5| and then turned 90 to bear against the supportinglugs. The cap screw is turned from the high temperature side of thebaflle to engage the block and hold the parts assembled. The refractoryat the front side can be easily removed to afford access to the capscrew, if the block requires renewal.

The rear furnace section has a substantially greater height andunobstructed volume than the front section, resulting in a substantiallength of furnace gas travel in heat transfer relation to radiant heatabsorbing surface. The vertical arrangement and upwardly flaringformation of this section and the drop in gas velocity facilitate theseparation of ash particles in suspenash separating in the rear sectionby gravity and the change in direction of' the gases will be mostly in adry granular state and can be easily handled. The descending ash eitherfalls directly into the hopper 55 or slides down the surface of theinclined wall 14 thereto. The ash is quenched in the pit 56- andaccumulates in the bottom thereof, from which it is removed as desiredby means of the bucket hoist- 83, as indicated in Fig. 1

Due to the arrangement and construction of the furnace bailie and slagscreen, the boiler tube bank 15 and auxiliary heating surface will becompletely shielded from direct radiant heat from the high temperaturesection. A high percentage of the ash content of the fuel is recoveredin the high temperature section and much of the remaining ash insuspension caused to separate while passing through the low temperaturesection. Any ash particles which reach the boilertubes will have losttheir troublesome temperatures and can be easily blown off the tubes.

One installation of the steam boiler illustrated has a designed capacityof 500,000 lbs. of steam per hour at 1450 lbs. per sq. in. pressure and935 F. total steam temperature. The designed heat release per front footof furnace is 31,400,- 000 B. t. u.', with a heat release per cubic footof 38,000 B. t. u. for the total furnace and 100,000 B. t. u. for thehigh temperature section. Continuous slag removal is contemplated forcoals having ash fusion temperatures up to 2800 F. Approximately 60% ofthe fuel ash content will be retained in the furnace. The furnace isthus virtually independent of the type of coal used.

While in accordance with the provisions of the statutes I haveillustrated and described herein the best form of my invention now knownto, me, those' skilled in the art will understand that changes may bemade in the method of operation and the form of the apparatus disclosedwithout departing from the spirit of the invention covered by theclaims, and that certain features of the invention may sometimes be usedto adperature section, heat absorbing means lining said high temperaturesection and proportioned aacarea to maintain a normal mean temperaturetherein above the fuel ash fusion temperature, a closed floor for saidhigh temperature-section constructed to support a layer of molten slag,

-means for introducing a stream of finely divided solid fuel into saidhigh temperature section and burning the same in suspension thereinatftemperatures above the fuel ash fusion temperature, a group ofvertically disposed tubes extending upwardly from said floor and havingportions so bent and arrangedas to form a slag drain opening betweenadjacent tubes at the floor level of said high temperature. section,means forming a slag dam between other pairs of adjacent tubes, andmeans forming an ash receiving space at the bottom of said lowtemperature section and constructed to receive molten slag from saidslag drain opening.

2. A steam generator unit comprising a furnace chamber having a hightemperature section and a low temperature section laterally adjoiningsaid high temperature section, a steam boiler receiving furnace gasesfrom said low temperature section, heat absorbing means lining theboundary surfaces of said high temperature section and proportioned tomaintain a normal mean temperature therein above the fuel ash fusiontemperature and including a closed fluid cooled floor constructed tosupport a layer of moltenslag, means for downwardly introducing a streamof finely divided solid fuel into the upper end of said high temperaturesection and burning the same in suspension therein at temperatures abovethe fuel ash fusion temperature, a group of vertically disposedrefractory covered tubes extending upwardly from one end of said floorand arranged to form a fluid cooled screen having transverselyspaced gasflow passages therein terminating at their lowerends above the floorlevel of said high temperature section for furnace gas flow between saidsecnace chamber having a high temperature sec-.

tion and a low temperature section laterally adjoining said hightemperature section, a' steam boiler receiving furnace gases from theupper end of said low temperature section, heat absorbing means liningthe boundary surfaces of absorbing means lining the boundary surfaces ofsaid low temperature section and proportioned to maintain a normal meantemperature therein below said fuel ash fusion temperature, and

- means forming an ash receiving space at the bottom of said lowtemperature section and con-- structed to receive molten slag from saidslag drain opening and ash separated in saidlow temperature section. V v

4. A steam generator unit comprising a furnace chamber having a hightemperature section and a low temperature section laterally adjoin-' ingsaid high temperature section, saidlow temperature section extendingabove, and having a substantially greater unobstructed volume than saidhigh temperature'section, a steam boiler receiving furnace gases fromtheupper end of said low temperature section, heat absorbing means liningthe boundary surfaces of said high temperature section and proportionedto maintain a normal mean temperature therein above the fuel ash fusiontemperature and including a closed fluid cooled floor constructed tosupport a layer of molten slag, means for downwardly introducing astream of finely divided solid fuel into the upper end-of said hightemperature section and burning the same in suspension therein attemperatures above the fuel ash' fusion temperature, a group ofvertically disposed refractory covered tubes extending upwardly from oneend of said floor and arranged to form a fluid cooled screen havingtransversely spaced gas flow passages therein for furnace gas flowbetween said sections, some of said screen tubes having obliquelyaligned bent portions with a closed intertube space arranged to form ashielded slag drain opening at the floor level of said high temperaturesection, heat absorbing means lining the boundary surfaces of said lowtemperature section and proportioned to maintain a normal meantemperature therein below said fuel ash fusion temperature, and. meansforming an ash receiving space at the bottom of said.- low temperaturesection and constructed to receive molten slag from said slag drainopening and ash separated in said low temperature. section. I

5. A furnace for burning pulverized fuel comprising walls defining afurnace chamber, means said high temperature section and proportioned tomaintain a normal mean temperature therein'above the fuel ash fusiontemperature and including a closed fluid cooled floor constructed tosupport a layer of molten slag, means for introducing a stream of finelydivided solid fuel into said high temperature section and buming thesame in suspension therein at temperatures above the fuel ash fusiontemperature, a

row of vertically disposed refractory covered for burning pulverizedfuel in suspension in said furnace chamber,a closed fluid cooled floorconstructed to support a layer of molten slag, and a row of verticallydisposed tubes at one side of said furnace chamber extending to saidfloor, spaced groups of adjacent tubes having aligned bent portions bentout of the plane of said row adjacent said'floor, metallic projectionson said tube bent portions, and refractory material closing theintertube space of the bent portions of each group and held in contacttherewith by said projections;

6. A furnace for burning pulverized fuel comprisingwalls defining afurnace chamber, means for burning pulverized fuel in suspension in saidfurnace chamber, a closed fluid cooled floor con structed to support alayer of molten slag,' and a row of vertically disposed tubes at oneside of said furnace chamber extending to said floor, groups of adjacenttubes having aligned por-' tions bent out of the plane of said row withthe bent portions arranged relative to adjacent tubes in said row toform shielded flow passages therebetween, metallic projections mountedon said tube bent portions, and refractory material closing theintertube space of the bent portions form a fluid cooled screen at oneside of said furnace chamber extending to said floor, certain adjacenttubeshaving refractory covered portions bent out of the plane of saidrow with the bent portions in alignment to partly define a flow passagethrough said screen. shielded by said tube bent portions.

8. A furnace for burning-pulverized fuel comprising walls defining afurnace chamber, means for burning pulverized fuel in suspension in'saidfurnace chamber, a closed floor constructed to support a layer of moltenslag, and a row of vertically disposed tubes arranged to form a fluidcooled screen at one side of said furnace chamber, certain adjacenttubes having portion's bent to progressively greater distances out ofsaid tube row with the bent portions in alignment in a plane oblique tothe plane of the tube row to partly define a slag drain passage throughsaid screen at the floor level.

9. A furnace for burning pulverized fuel comprising walls defining afurnace chamber, means for burning pulverized fuel in suspension in saidfurnace chamber, a closed fluid cooled floor constructed to support alayer of molten slag, and a row of vertically'disposed, refractorycovered studded tubes arranged to form a fluid cooled screen at one sideof said furnace chamber; certain pairs of adjacent tubes having lowerportions bent out of the plane of said row withthe bent portions inalignment in a plane parallel to the plane of said row to form gas flowpassages through said screen shielded from furnace radiant heat by saidtube bent portions, the lower ends of some of said tubes having portionswent in alignment in a plane oblique to the plane )f said tube row todefine a slag drain opening in said screen at the levelof said floor topermit molten slag to flow therethrough.

10. A furnace for burning finely divided solid fuel comprisingvertically disposed front, rear and side walls defining a furnacechamber, an arch extending rearwardly from said front wall over thefront section of said furnace chamber, means forming a transverse baflleextending :downwardly from said arch and terminating above the furnacebottom to separate a front high temperature section and a rear lowtemperature section communicating adjacent the furnace bottom, means insaid arch for introducing a stream of finely divided solid fuel into theupper end of and burning the same in suspension in said front section attemperatures above the fuel ash fusion temperature, a closed over thefront section of saidlfurnace chamber.

means forming a transverse bame extending downwardly from said arch andterminating above the furnace bottom to separate a front hightemperature section and a rear low temperature section communicating attheir lower ends, means in said arch for introducing a stream of finelydivided solid fuel downwardly into the upper e1 .1 of and burning thesame in suspension in said high-temperature section at furnacetemperatures above the fuel ash fusion temperature, heat absorbing meanslining the boundary surfaces of said high temperature section andconstructed to maintain a normal mean temperature therein above the fuelash fusion temperature including a closed fluid cooled fio'or constructed to receive a layer of molten slag, heat absorbing means liningthe boundary surfaces of said low temperature section and constructed tomaintain a normal mean temperature therein below the fuel ash fusiontemperature, a group of vertically disposed refractory covered tubesbetween the lower end of said balile and the furnace bottom arranged toform a fluid cooled screen having a slag drain opening therein adjacentthe fioor level in said high temperature section, and a fluid cooledhopper below said low temperature section constructed to receive dry ashseparated in said low temperature section and molten slag flowingthrough said slag drain opening from said high temperature sectionfloor.

12. In a furnace having a furnace chamber divided into a hightemperature zone and a laterally adjoining low temperature zonecommunicating therewith, themethod of burning a finely divided solidfuel and eliminating a high percentage of the ash content of the fuel inthe furnace chamber which comprises downwardly discharging a stream ofthe fuel and air for combustion into and burning the fuel in suspensionin said high temperature zone at temperatures above the fuel ash fusiontemperature, collecting molten slag separated in said high temperaturezone in the lower portion of said zone, directing the furnace gases fromthe lower part of said high temperature zone into the lower part of saidlow temperature zone, cooling the. furnace gases to a temperature belowthe fuel ash fusion temperature while passing upwardly through said lowtemperature zone, and draining the molten slag collecting in said hightemperature zone into the lower portion of said low temperature zone.

13. In a furnace having a furnace chamber divided into a hightemperature zone and a low fluid cooled floor below said front sectioncontemperature zone communicating at their lower ends, the method ofburning a finely divided solid fuel and eliminating a high percentage ofthe ash content of the fuel in the furnace chamber which comprisesintroducing a stream of the fuel and air for combustion into the upperend of and burning the fuel in suspension while pass ing downwardly insaid high temperature zone at temperatures above the fuel ash fusiontem-. perature, collecting molten slag separated in said hightemperature zone in the lower portion of said zone, directing thefurnace gases from said high temperature zone into said low temperaturezone through shielded high velocity flow passages,

cooling the furnace gases and suspended ash tc a temperature below thefuel ash fushion temperature while passing upwardly through said lowtemperature zone, and draining the molten slag from said hightemperature zone'ithrough said flow passages into the lower portion ofsaid low temperature zone.

centage of the ash content of the fuel in the' furnace chamber whichcomprises downwardly discharging a stream of the fuel and air for,combustion into and burning the fuel in suspension in said hightemperature zone at temperatures above the fuel ash fusion temperature,collecting molten slag separated in said high temperature zone in thelower portion of said zone,

part of said low temperature zone through high velocity flow passages,cooling the furnace gases and suspended ash to a temperature below thefuel ash fusion temperature while passing upwardly at-a lower velocitythrough said low temperature zone, and collecting'the ash separated insaid low temperature zone and draining the molten slag collecting insaid high temperature zone into the lower portion of said low temperature zone.

15. In a fluid heater, a wall having its opposite sides adapted to beexposed in operation to different temperature conditions and comprisinga row of spaced fluid heating tubes, a series of metallic projectionsmounted on the high temperature side of said tubes and projecting intothe intertube spaces, refractory material held by said projections incontact with said tubes and arranged to close the intertube spaces atthe high temperature side of said-tubes, metallic blocks at the lowtemperature side of said tubes, and'means for holding said blocks inthermal contact with said tubes.

16. In a fluid heater, a wall having its opposite ing a row of spacedheating fluid tubes, a series of metallic projections mounted on saidtubes and projecting into the intertube spaces, refractory materialbetween said projections in contact with said tubes and arranged toclose the intertube spaces at the high temperature side of said tubes,lugs mounted on said tubes and extending into the intertube spaces,metallic blocks at the low temperature side of said tubes, and meansengaging said lugs and blocks to hold said blocks in thermal contactwith said tubes.

18. In a furnace, a furnace ballie having its opposite sides adapted tobe exposed in operation to different furnace temperature conditions andcomprising a row of vertically disposed spaced fluid heating tubes, aseries of metallic projections mounted on the high temperature side ofsaid tubes and projectinginto the intertube spaces, refractory materialbetween said projections covering the high temperature side of saidtubes and arranged to close the intertube spaces at the high temperatureside of said tubes, lugs welded on said tubes and extending 1 tubes, andclamping means engaging said lugs into the intertube spaces, metallicblocks arranged to cover; the low temperature side of said and blocks tohold said blocks in thermal contact with said tubes.

19. A steam generator unit comprising a furnace chamber having a hightemperature section and a low temperature section laterallyadjoiningsaid high temperature section, a steam boiler receiving furnace gasesfrom said low temperature section, means for burning finely dividedsolid fuel in suspension in said high temdirecting the furnace gasesfrom the lower part of said high temperature zone into the lowerperature section and maintaining a normal mean temperature therein abovethe fuel ash fusion temperature, a closed floor for said hightemperature section constructed to supports layer of molten slag, a rowof water tubes extending along and fluid cooling said floor, meansforming an ash receiving space at the bottom of said low temperaturesection and constructed to receive molten slag from one end of saidfloor, means forming a fluid cooled screen extending upwardly from theslag discharge end of said floor and having spaced gas flow passagestherein for furnace gas flow between said sections and lower tubeportions bent to form spaced slag drain openings therebetween, and meansform- I ing a slag dam at the slag discharge end of said floor.

20. A steam generator unit comprising a furnace chamber having a hightemperature section and a low temperature section laterally adjoiningsaid high temperature section, a steam boiler receiving furnace gasesfrom said low temperature section, means for burning finely dividedsolid fuel in suspension in said high temperature section andmaintaining a normal mean temperature therein above .the fuel ash fusiontemperature, a flat sloping floor for said high temperature sectionconstructed to support a layer of molten slag, a row of inclined watertubes extending along and fluid cooling said floor, means forming an ashreceiving space at the bottom of said low temperature section andconstructed to receive molten slag from the lower end of said floor,means forming a slag receiving furnace gases from said low temperaturesection, a closed floor for said high temperature section constructed tosupport a layer of molten slag and discharge the same at one endthereof, heat absorbing means lining the boundary surfaces of said hightemperature section and proportioned to maintain a normal meantemperature therein above the fuel ash fusion temperature, said heatabsorbing meansincluding a row of vertically disposed water tubesextending upwardly from the slag discharge end of said floor and havingportions grouped to form transversely spaced gas flow passages thereinfor furnace gas flow between said sections and lower tube portionsdifferently grouped to form a substantially lesser number of slagdischarge openings therebetween for the slag on said floor, means forintroducing finely divided solid fuel into said high temperature sectionand burning the same in suspension therein at temperatures "abovethefuel ash fusion temperature, and means forming an asr receiving spaceat the bottom of said low temperature section and constructed to receivemolten slag from said slag discharge opening or openings. v

22. A steam generator unit comprising a furnace chamber having a hightemperature section and a low temperature section laterally adjoiningsaid high temperature section, a steam boiler receiving furnace gasesfrom said low temperature section, a sloping floor for said hightemperature section constructed to support a layer of molten slag, heatabsorbing means lining the boundary surfaces of said. high temperaturesection and proportioned to maintain a normal mean temperature thereinabove the fuel ash fusion temperature, said heat absorbing meansincluding a row of water tubes extending along said high temperaturesection floor and a group of vertically disposed water tubes extendingupwardly from the lower end of said floor and arranged to form a fluidcooled screen having transversely spaced gas flow passages therein forfurnace gas flow between said sections, means for introducing finelydivided solid nace chamber having a high temperature section and a lowtemperature section laterally adjoining said high temperature section, asteam boiler receiving furnace gases from said low temperature section,a closed floor for said high temperature section constructed to supporta layer of molten slag, heat absorbing means lining the boundarysurfaces of said high temperature section and proportioned to maintain anormal mean temperature therein above the fuel ash fusion temperature,said heat absorbing means including a row of water tubes extending alongsaid high temperature section floor and a group of vertically disposedwater tubes extending upwardly from the slag discharge end of said floorand arranged to form a fluid cooled screen having transversely spacedgas flow passages therein for furnace gas flow between said sections,means for downwardly introducing a stream of finely divided solid fuelinto the upp r end of said high temperature section and burning the samein suspension therein at temperatures above the fuel ash fusiontemperature, a transversely extending header below the level of the slagdischarge end of said floor and directly connected to the lower ends ofsaid floor and screen tubes, said header and tube connections theretobeing arranged to. minimize relative movement of said floor and screentubes adjacent the floor level, means for connecting said header intothe circulation system 'of said steam boiler, and means forming an ashreceiving space at the bottom of said low temperature section andconstructed to receive molten slag from said floor.

ROLFE SHELLENBERGER.

